VizualAge, a new computer software tool for analysing U‐Pb data obtained by laser ablation‐inductively coupled plasma‐mass spectrometry, was developed. It consists of a data reduction scheme (DRS) ...for Iolite (a general mass spectrometry data analysis tool) as well as visualisation routines. In addition to the U/Pb and Th/Pb ages calculated by Iolite’s U‐Pb geochronology DRS, VizualAge also calculates 207Pb/206Pb ages and common Pb corrections for each time‐slice of raw data. Importantly, VizualAge allows one to display a live concordia diagram for visualising data on such a diagram as an integration interval is being adjusted. This provides instantaneous feedback regarding discordance, uncertainty, error correlation and common Pb. Several zircon data sets were used to illustrate how the live concordia could be used as a powerful inspection tool, revealing a single analysis to consist of zones of concordance, metamict areas, as well as inherited cores or younger overgrowths. VizualAge also constructs histograms, conventional and Tera‐Wasserburg type concordia diagrams, as well as 3D U‐Th‐Pb and total U‐Pb concordia diagrams. The precision and accuracy of data reduced with VizualAge are demonstrated with examples of the Plešovice, Temora‐2 and Penglai zircon reference materials. Data for zircon from the Long Lake Batholith (Wyoming craton) were used to illustrate how VizualAge calculated common Pb corrections and helped to expose as yet unexplained difficulties with accurately determining 204Pb.
VizualAge, un nouvel outil informatique pour l’analyse des données U‐Pb obtenues avec un système d’ablation laser reliée à un spectromètre de masse couplée à un plasma inductif a été développé. Il se compose d’un programme de réduction des données (DRS) pour Iolite (un outil d’analyse des données générées par la spectrométrie de masse) ainsi que de routines de visualisation. En plus des âges U/Pb et Th/ Pb calculés par le DRS de géochronologie U‐Pb Iolite, VizualAge calcule également les âges 207Pb/206Pb et les corrections du Pb commun pour chaque tranche de temps des données brutes. Surtout, VizualAge permet d’afficher un diagramme Concordia en direct permettant de visualiser les données sur un tel diagramme pendant qu’un intervalle d’intégration est en cours d’ajustement. Ceci fournit une rétroaction instantanée sur la discordance, l’incertitude, l’erreur de corrélation et le Pb commun. Plusieurs bases de données sur zircon ont été utilisés pour illustrer la façon dont la Concordia en direct pourrait être utilisé comme un outil d’inspection puissant, révélant qu’une seule analyse peut représenter des zones de concordance, des zones métamictes, ainsi que des noyaux hérités ou des surcroissances plus jeunes. VizualAge construit également des histogrammes, des diagrammes concordia de type classique et de type Tera‐Wasserburg, ainsi que des diagrammes concordia 3D U‐Th‐Pb et U‐Pb total. La précision et l’exactitude des données réduites avec VizualAge sont démontrées par l’exemple des zircons de référence Plešovice, Temora‐2 et Penglai. Les données sur zircons provenant du batholite de Long Lake (craton du Wyoming) ont été utilisés pour illustrer comment VizualAge calcule les corrections du Pb commun et contribue à mettre en évidence des difficultés encore inexpliquées dans la détermination précise du 204Pb.
As base metals, zinc and lead are widely developed in various types of deposits. Zinc and lead also form various types of independent deposits and are associated with a variety of critical metals. ...Zn-Pb deposits occupy an important position in the world, including volcanic-hosted massive sulphide (VHMS/VMS), magmatic–hydrothermal-associated skarn and/or epithermal types, sediment-hosted types (e.g., clastic-hosted sedimentary exhalative, SEDEX; carbonate-hosted Mississippi Valley type, MVT; sandstone-hosted type, SST; and shale-hosted type), and hydrothermal vein types. This Special Issue reprint aims to provide a comprehensive understanding of Zn-Pb deposits and associated critical metals, and promote global prospecting.
Dating and geochemical analyses of detrital minerals (mainly zircons) combined with traditional methods, such as heavy minerals and sandstone modes, are a powerful tool in paleogeographic and ...paleotectonic research and industrial applications.
Apatite is a common U- and Th-bearing accessory mineral in igneous and metamorphic rocks, and a minor but widespread detrital component in clastic sedimentary rocks. U–Pb and Th–Pb dating of apatite ...has potential application in sedimentary provenance studies, as it likely represents first cycle detritus compared to the polycyclic behavior of zircon. However, low U, Th and radiogenic Pb concentrations, elevated common Pb and the lack of a U–Th–Pb apatite standard remain significant challenges in dating apatite by LA-ICPMS, and consequently in developing the chronometer as a provenance tool.
This study has determined U–Pb and Th–Pb ages for seven well known apatite occurrences (Durango, Emerald Lake, Kovdor, Mineville, Mud Tank, Otter Lake and Slyudyanka) by LA-ICPMS. Analytical procedures involved rastering a 10
μm spot over a 40
×
40
μm square to a depth of 10
μm using a Geolas 193
nm ArF excimer laser coupled to a Thermo ElementXR single-collector ICPMS. These raster conditions minimized laser-induced inter-element fractionation, which was corrected for using the back-calculated intercept of the time-resolved signal. A Tl–U–Bi–Np tracer solution was aspirated with the sample into the plasma to correct for instrument mass bias. External standards (Plešovice and 91500 zircon, NIST SRM 610 and 612 silicate glasses and STDP5 phosphate glass) along with Kovdor apatite were analyzed to monitor U–Pb, Th–Pb, U–Th and Pb–Pb ratios
Common Pb correction employed the
207Pb method, and also a
208Pb correction method for samples with low Th/U. The
207Pb and
208Pb corrections employed either the initial Pb isotopic composition or the Stacey and Kramers model and propagated conservative uncertainties in the initial Pb isotopic composition. Common Pb correction using the Stacey and Kramers (1975) model employed an initial Pb isotopic composition calculated from either the estimated U–Pb age of the sample or an iterative approach. The age difference between these two methods is typically less than 2%, suggesting that the iterative approach works well for samples where there are no constraints on the initial Pb composition, such as a detrital sample. No
204Pb correction was undertaken because of low
204Pb counts on single collector instruments and
204Pb interference by
204Hg in the argon gas supply.
Age calculations employed between 11 and 33 analyses per sample and used a weighted average of the common Pb-corrected ages, a Tera–Wasserburg Concordia intercept age and a Tera–Wasserburg Concordia intercept age anchored through common Pb. The samples in general yield ages consistent (at the 2σ level) with independent estimates of the U–Pb apatite age, which demonstrates the suitability of the analytical protocol employed. Weighted mean age uncertainties are as low as 1–2% for U- and/or Th-rich Palaeozoic–Neoproterozoic samples; the uncertainty on the youngest sample, the Cenozoic (31.44
Ma) Durango apatite, ranges from 3.7–7.6% according to the common Pb correction method employed. The accurate and relatively precise common Pb-corrected ages demonstrate the U–Pb and Th–Pb apatite chronometers are suitable as sedimentary provenance tools. The Kovdor carbonatite apatite is recommended as a potential U–Pb and Th–Pb apatite standard as it yields precise and reproducible
207Pb-corrected,
232Th–
208Pb, and common Pb-anchored Tera–Wasserburg Concordia intercept ages.
► Rapid, accurate U–Pb and Th–Pb apatite dating is possible by single collector LAICPMS. ► Apatite standards yield ages consistent with independent estimates of the U–Pb age. ► Th–Pb dating yields much promise, particularly in high Th samples. ► Accurate common Pb correction can be achieved without measuring 204Pb. ► This study opens the possibility of detrital apatite dating for sedimentary provenance analysis.
Authigenic xenotime (YPO4) and monazite ((Ce, La, Nd)PO4) are common trace components in siliciclastic sedimentary rocks, where they can form under diverse geological processes such as ...low-temperature early diagenesis or hydrothermal activities or later low grade metamorphism. Authigenic xenotime and monazite could carry distinctive geochemical fingerprints. By virtue of their commonly high U and Th concentrations (commonly 100–1000 ppm) and high closure temperature for U/Th-Pb isotope systems (700–800 °C), dates from authigenic phosphate are frequently used to constrain the depositional age of sedimentary rocks. Their tiny size (commonly <20 μm but can be occasionally up to about 1 mm in diameter for large monazite nodules) requires SEM-BSE imaging to locate for in situ high spatial and mass resolution SIMS U-Pb/Pb-Pb dating analyses. Their variable chemical compositions, particularly xenotime, require multiple (at least three) matrix-matching standards to correct UPb fractionation. Interpretation of radiometric ages sometimes encounters difficulties because of diverse origins of phosphates including diagenetic, hydrothermal, and detrital origins. An integrated petrographic and geochemical study can aid in telling apart diagenetic xenotime/monazite from their hydrothermal and detrital counterparts, thereby correctly applying them to constrain the depositional age of sedimentary rocks.
Within the last decade, the high and continuing demand for precious and base metals, as well as critical elements, has prompted a global rush on a scale never before seen. This eventually resulted in ...the demand for considerable innovation and improvement in mineral deposit genetic modelling and ore formation regimes for the many different types of gold deposits, now recognized, and paralleled by the wide employment of exploration techniques and a rapid expansion of geological databases.
This Special Issue will show case studies of porphyry polymetal systems, orogenic gold formations, water–rock reaction, ore-forming structure evolution, mineralogy and petrology of ore deposit, ore formation regime, geochronology and geochemistry of ore deposit, ore-forming evolution, mineral exploration and cutting-edge technology in ore deposit study.
The decorrelation of the orientation of the event-plane angles in the initial state of relativistic Pb–Pb and p–Pb collisions, the “torque effect”, is studied in a model of entropy deposition in the ...longitudinal direction involving fluctuations of the longitudinal source profile on large scales. The radiation from a single wounded nucleon is asymmetric in space–time rapidity. It is assumed that the extent in rapidity of the region of deposited entropy is random. Fluctuations in the deposition of entropy from each source increase the event-plane decorrelation: for Pb–Pb collisions the change is moderate, while for p–Pb collisions the mechanism is absolutely essential to generate any sizable decorrelation. We also show that the experimental data for rank-four flow may be explained via folding of the elliptic flow. The results suggest the existence of long range fluctuations in the space–time distribution of entropy in the initial stages of relativistic nuclear collisions.
The LA‐ICP‐MS U‐(Th‐)Pb geochronology international community has defined new standards for the determination of U‐(Th‐)Pb ages. A new workflow defines the appropriate propagation of uncertainties ...for these data, identifying random and systematic components. Only data with uncertainties relating to random error should be used in weighted mean calculations of population ages; uncertainty components for systematic errors are propagated after this stage, preventing their erroneous reduction. Following this improved uncertainty propagation protocol, data can be compared at different uncertainty levels to better resolve age differences. New reference values for commonly used zircon, monazite and titanite reference materials are defined (based on ID‐TIMS) after removing corrections for common lead and the effects of excess 230Th. These values more accurately reflect the material sampled during the determination of calibration factors by LA‐ICP‐MS analysis. Recommendations are made to graphically represent data only with uncertainty ellipses at 2s and to submit or cite validation data with sample data when submitting data for publication. New data‐reporting standards are defined to help improve the peer‐review process. With these improvements, LA‐ICP‐MS U‐(Th‐)Pb data can be considered more robust, accurate, better documented and quantified, directly contributing to their improved scientific interpretation.
La communauté internationale de la géochronologie LA‐ICP‐MS U‐(Th‐)Pb a défini les nouvelles normes pour la détermination des âges U‐(Th‐)Pb. Un nouveau flux de travail définit la propagation adéquate des incertitudes pour ces données, en identifiant les composants aléatoires et systématiques. Seules les données avec des incertitudes relatives à l'erreur aléatoire devraient être utilisées dans les calculs des moyennes pondérées des âges de la population; les composantes de l'incertitude pour les erreurs systématiques sont propagées après cette étape, empêchant leur réduction erronée. En suivant ce protocole amélioré pour la propagation de l'incertitude, les données peuvent être comparées à différents niveaux d'incertitude pour mieux résoudre les différences d’âge. Les nouvelles valeurs pour les matériaux de référence zircon, monazite et titanite sont définies (basée sur ID‐TIMS) après les corrections du plomb commun et les effets de l'excès en 230Th. Ces valeurs reflètent plus fidèlement le matériau échantillonné lors de la détermination des facteurs d’étalonnage par analyse LA‐ICP‐MS. Des recommandations sont faites pour représenter graphiquement des données avec seulement des ellipses d'incertitude à 2s et pour soumettre ou pour citer des données de validation avec les données de l’échantillon lors de la soumission des données pour publication. Les nouvelles normes de déclaration des données sont définies pour améliorer le processus d'évaluation par les pairs. Grâce à ces améliorations, les données LA‐ICP‐MS U‐(Th)‐Pb peuvent être considérés comme plus solides, exactes, mieux documentées et quantifiées, contribuant ainsi à une meilleure interprétation scientifique.
Key points
New community‐derived LA‐ICP‐MS U‐(Th‐)Pb geochronology uncertainty propagation workflow defined, allowing better representation of absolute age uncertainties and better resolution of relative age differences within samples.
New reference values defined for commonly used U‐Pb reference materials.
New data‐reporting standards defined for more rigorous data presentation and peer review.
Monazite can be used for U–Pb and Th–Pb dating of a wide variety of rocks and geological processes, particularly metamorphism. In many instances ion microprobe analysis is the preferred method for ...dating monazite, combining good analytical precision with μm-scale spatial resolution. However, ion microprobe dates can be compromised by matrix effects on the ionisation efficiencies of different secondary ionic species, which can bias monazite Pb
+/ThO
n
+ and Pb
+/UO
n
+ data by as much as ∼
40% and ∼
30%, respectively, for known monazite compositions. These effects appear to be entirely attributable to the sputtering process, in which case similar effects exist in data from all ion probes. The effects on data ratios are modified, sometimes exacerbated or reversed, when data are subjected to the correlation-based Pb/Th and Pb/U calibrations that are now commonly used. One-dimensional calibrations of
206Pb
+/
270UO
2
+ and
208Pb
+/
264ThO
2
+ are recommended. Corrections derived from data for a suite of reference materials with diverse compositions can reduce biases in
208Pb/
232Th ages to <∼2% and in
206Pb/
238U ages to <∼1%. The matrix effects come predominantly from variations in the concentrations of Th, U, Pb, light rare earth elements (LREE) and Y. La/Ce is an effective proxy for REE composition in many monazites, but for some monazites it would also be necessary to monitor Nd. Matrix corrections can be applied without measuring all LREE, using ion probe data alone. Other interacting data complications, such as Pb/Pb fractionation and an isobar at
204Pb
+, can be addressed without iterative data reduction.
Zircon has played a critically important role in our understanding of the growth and evolution of the Earth. The U–Pb isotope system as preserved in zircon, more than any other mineral or method, has ...provided the most precise geochronological constraints for timing of geological events and processes on the Earth. More recently, technological advances have allowed for the precise determination of the Hf isotope composition of zircon, a geochemical tracer that has provided important details on the Earth's chemical evolution, in particular the evolution of the crust–mantle system. When combined, U–Pb ages and Hf isotopes in zircons hold the promise of providing unprecedented resolution in the timing and processes of planetary differentiation. Nowhere is this more true than for the early history of the Earth, where younger tectonothermal processes have compromised the isotope information in bulk rock samples. With the promise of this integrated technique, however, lies numerous potential pitfalls in the acquisition and interpretation of these data. In this paper we review several important issues related to unraveling the complexities of integrated U–Pb age and Hf isotope datasets, especially with respect to understanding crust–mantle evolution. In particular, we address the potential difficulty of assigning accurate initial Hf isotope compositions as well as some of the inherent problems associated with so-called “depleted-mantle model ages”. Finally, we make some suggestions regarding the optimum analytical approach and presentation of the Hf (and Nd) isotope data to obtain the clearest record of Earth's chemical evolution.
•We review several issues related to complexities in integrated U-Pb age and Hf isotope datasets, especially related to the record of crust-mantle evolution.•We address the potential difficulty of determining accurate initial Hf isotope compositions and epsilon Hf values.•We identify the inherent problems associated with “depleted-mantle model ages”.•We suggest the best analytical approach to, and presentation of, Hf (and Nd) isotope data to obtain the clearest record of Earth’s chemical evolution.
PDF
